The species of Ash are frequently misidentified, at least
in part due to the mistaken impression created in some popular tree
books and perpetuated in introductory classes that the species can be
easily distinguished by a single character such as the bark. With experience
many individuals can be accurately identified, but it is best to consider
a combination of several characters and to acknowledge that some leaves,
branches or even entire trees may not work well in any given key.

Fraxinus americana tends to have clearly
stalked leaflets with whitened undersides. The leaflets of F.
pennsylvanica have short stalks and those of F. nigra are
sessile (they have no stalk), and both lack a conspicuously whitened
undersurface. On well developed branches of Fraxinus americana
the leaf scars are often concave
along the upper edge and the buds originate well within the curved
portion of the leaf scar. The leaf scars of Green and Black ash are
not concave along the upper edge or only slightly so.

Fraxinus americana tends to occur primarily in
upland forests, often with Acer saccharum. F. nigra is
most often restricted to clearly wet sites. F. pennsylvanica
is by far the commonest species of Ash in the southern two thirds of
the state and often thrives in disturbed, young woods, both upland and
lowland, and in old fields and other disturbed, open sites. The autumn
leaf color of healthy F. americana trees often has a rich purplish
tone or a distinctive reddish brown color, compared to the mostly yellow
autumn leaves of F. nigra and F. pennsylvanica.